2021MNRAS.505..359B

Predicting how a young planet shapes the gas and dust emission of its parent disc is key to constraining the presence of unseen planets in protoplanetary disc observations. We investigate the case of a 2 Jupiter-mass planet that becomes eccentric after migrating into a low-density gas cavity in its parent disc. 2D hydrodynamical simulations are performed and post-processed by 3D radiative transfer calculations. In our disc model, the planet eccentricity reaches ∼0.25, which induces strong asymmetries in the gas density inside the cavity. These asymmetries are enhanced by photodissociation and form large-scale asymmetries in ¹²CO J=3-2 integrated intensity maps. They are shown to be detectable for an angular resolution and a noise level similar to those achieved in ALMA observations. Furthermore, the planet eccentricity renders the gas inside the cavity eccentric, which manifests as a narrowing, stretching and twisting of iso-velocity contours in velocity maps of ¹²CO J=3-2. The planet eccentricity does not, however, give rise to detectable signatures in ¹³CO and C¹⁸O J=3-2 inside the cavity because of low column densities. Outside the cavity, the gas maintains near-circular orbits, and the vertically extended optically thick CO emission displays a four-lobed pattern in integrated intensity maps for disc inclinations ≳30^*. The lack of large and small dust inside the cavity in our model further implies that synthetic images of the continuum emission in the sub-millimetre, and of polarized scattered light in the near-infrared, do not show significant differences when the planet is eccentric or still circular inside the cavity.